Re: [Help-gsl] Re: Reg :: Error in declaring typedef of template class

[Akanksh Vashisth]

Sorry about the earlier post, made a mistake there, only the base class
non-virtual destructor shall be called, and the overhead will be the extra
constructor of the derived class.

2009/11/11 Akanksh Vashisth <address@hidden>

> Hello Sumit,
>
> I would advice against using this form:
>
> template<class T> class m_signal_out_if<T> : public m_signal_inout_if<T>
> {};
>
> to do a pseudo-typedef, because here the assumption is that m_signal_inout_if
> has a virtual destructor, because if m_signal_inout_if does not have a
> virtual destructor, than the destruction of the base class shall not be
> correct and might result in memory leaks if any of the base classes free up
> allocated memory while destructing.
>
> So this technique works fine if the base class is known to not do any
> allocations (and you are happy with undefined destruction behaviour) or if
> it is known that the base class has a virtual destructor. Even so, the
> overhead of the compiler generating the constructor and destructor of this
> derived class is not acceptable or needed.
>
> And yes, C++0x will have support for templated typedefs.
>
> 2009/11/11 Sumit Adhikari <address@hidden>
>
>> Hello Akanksh,
>> I already had a solution through which I could have wrote(in fact I used
>> if you see mt other template classes) it as follows :
>>    template<class T> class m_signal_out_if<T> : public
>> m_signal_inout_if<T> {};
>> But I was curious about this specific implementation of templated typedef.
>> Well it is not supported. I do  know it is supported in c++0x.
>> Thanks for the reply,
>> Regards,
>> Sumit
>>
>>
>>
>> On Wed, Nov 11, 2009 at 2:37 PM, Akanksh Vashisth <address@hidden>wrote:
>>
>>> Also, if a collection of such typedefs is needed, something like this can
>>> be done ( but I would not suggest it as a default solution )
>>>
>>> template<typename T>
>>> struct MyType
>>> {
>>>      typedef  m_signal_inout_if < T >  m_signal_out_if;
>>>      typedef something_else_01<T> something_01;
>>>      typedef something_else_02<T> something_02;
>>> }
>>>
>>> and these can now be used as:
>>>
>>> MyType<SomeType1>:: m_signal_out_if variable_name_01;
>>> MyType<SomeType2>:: something_01   variable_name_02;
>>> MyType<SomeType3>:: something_02   variable_name_03;
>>>
>>> Hope this helps.
>>>
>>> Akanksh Vashisth
>>> Graphics Engine Programmer
>>> ArtVPS Ltd.
>>> Cambridge, UK
>>>
>>> 2009/11/11 Akanksh Vashisth <address@hidden>
>>>
>>> Hello Sumit,
>>>>
>>>> In C++ typedef of a template is illegal, so the following code
>>>>
>>>>
>>>> template < class T >
>>>> typedef  m_signal_inout_if < T >  m_signal_out_if < T > ;
>>>>
>>>> will not compile.
>>>>
>>>> If you do want to typedef something like this, you need to surround it
>>>> with a class definition, such as:
>>>>
>>>> template<typename T>
>>>> struct m_signal_out_if
>>>> {
>>>>     typedef m_signal_inout_if  < T > type;
>>>> }
>>>>
>>>> This can now be used as a type in the following way:
>>>>
>>>> m_signal_out_if<SomeType>::type variable_name;
>>>>
>>>> But seeing that the difference in you typedef name and the original
>>>> class name is not a lot, the overhead and complexity of this typedef is (in
>>>> my opinion) not acceptable.
>>>>
>>>> Hope this helps.
>>>>
>>>> Akanksh Vashisth
>>>> Graphics Engine Programmer
>>>> ArtVPS Ltd.
>>>> Cambridge, UK
>>>>
>>>> 2009/11/11 Sumit Adhikari <address@hidden>
>>>>
>>>> A little correction :
>>>>>
>>>>> # ifndef M_SIGNAL_OUT_IF_H_
>>>>> # define M_SIGNAL_OUT_IF_H_
>>>>>
>>>>>
>>>>> # include "m_signal_inout_if.h"
>>>>>
>>>>> template < class T > typedef  m_signal_inout_if < T >  m_signal_out_if
>>>>> < T > ;
>>>>>
>>>>>
>>>>>
>>>>> # endif /*M_SIGNAL_OUT_IF_H_*/
>>>>>
>>>>>
>>>>>
>>>>> --------------------------------------------
>>>>> Sumit Adhikari
>>>>> System Design Engineer
>>>>> austriamicrosystems AG
>>>>> Business Unit : Automotive
>>>>> Mob : 00-91-9885271710/00-91-9000161710
>>>>>
>>>>>
>>>>>
>>>>> On 11/11/2009 8:49 AM, Sumit Adhikari wrote:
>>>>>
>>>>>> Hello All,
>>>>>>
>>>>>> I have a template class like as follows :
>>>>>>
>>>>>> # ifndef M_SIGNAL_INOUT_IF_H_
>>>>>> # define M_SIGNAL_INOUT_IF_H_
>>>>>>
>>>>>> # include "m_signal_in_if.h"
>>>>>>
>>>>>> template < class T > class m_signal_inout_if : public m_signal_in_if <
>>>>>> T > {
>>>>>>   public :
>>>>>>      virtual void write (const T&) = 0 ;
>>>>>>      virtual void initialize(const T&) = 0;
>>>>>> };
>>>>>>
>>>>>>
>>>>>> # endif /*M_SIGNAL_INOUT_IF_H_*/
>>>>>>
>>>>>> I want to declare typedef of m_signal_inout_if and I have done it as
>>>>>> follows :
>>>>>>
>>>>>> # ifndef M_SIGNAL_OUT_IF_H_
>>>>>> # define M_SIGNAL_OUT_IF_H_
>>>>>>
>>>>>>
>>>>>> # include "m_signal_inout_if.h"
>>>>>>
>>>>>> template < class T > m_signal_inout_if < T >  m_signal_out_if < T > ;
>>>>>>
>>>>>>
>>>>>> # endif /*M_SIGNAL_OUT_IF_H_*/
>>>>>>
>>>>>>
>>>>>> But I am getting syntax error in this process.
>>>>>> Can anybody please tell me what is the wrong with it ?
>>>>>> Regards,
>>>>>>
>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Help-gsl mailing list
>>>>> address@hidden
>>>>> http://lists.gnu.org/mailman/listinfo/help-gsl
>>>>>
>>>>
>>>>
>>>
>>
>>
>> --
>>
>> --------------------------------------------
>> Sumit Adhikari
>> System Design Engineer
>> austriamicrosystems AG
>> Business Unit : Automotive
>> Mob : 00-91-9885271710/00-91-9000161710
>>
>
>